Catholics seeking an indulgence by climbing the Holy Stairs, which Jesus reputedly mounted before his crucifixion, may soon be asked to make a contribution to save the fixture's flaking frescoes.

Every year 2 million pilgrims in Rome get on their knees to shuffle up the 28 marble steps which tradition states once led to the room in Jerusalem where Pontius Pilate judged Christ before they were shipped to Italy in the fourth century.

Wooden boards protect the steps, with small openings revealing where Christ's blood reportedly stained the marble.

Researchers have warned the elaborate 16th-century frescoes that line the stairs and depict the passion of Christ and the crucifixion are fast disintegrating. "Plaster is detaching, there has been water infiltration, some paintwork is fading. Other parts are darkening due to soot from candles and we lack funding," said Mary Angela Schroth, an art curator who has studied the frescoes and is campaigning to raise the €1.6m (£1.4m) needed to safeguard them.

Funding from the Getty Foundation has been used up in studies and on the restoration of just one chapel in the sanctuary where the steps are housed, next to the basilica of St John Lateran. The lack of further income prompted the plan to ask for a small donation from pilgrims.

"It's painful to see the frescoes in this state," said Father Tito Amodei, a member of the Passionists, the black-robed order that runs the site.

"If just one pilgrim in two contributed a euro, the restoration could easily go ahead," he told Corriere della Sera. Climbing the steps earns an indulgence, which the church teaches can reduce time in purgatory once believers have confessed and been absolved of their sins. Outrage over the selling of indulgences in the Catholic church helped prompt the Protestant Reformation and is banned today.

Schroth said offering a euro at the Holy Stairs to aid restoration would not be compulsory. "There will be a small table where we answer questions and suggest a contribution, that's it," she said.

"The Passionists are more of a mystical order than businessmen and were reluctant to do this, so we worked hard to convince them."